1. Field of the Invention
The present invention relates to a cooling device for heat-generating elements that performs cooling of heat-generating elements by heat exchange action with a coolant.
2. Description of the Related Art
Semiconductor elements such as IGBTs are employed in equipment of various types including in particular power converters such as inverters. These semiconductor elements generate heat during operation of the equipment and so constitute heat-generating elements whose temperature rises to a considerable degree. A prescribed value (rating) is laid down in respect of the heat endurance temperature of these semiconductor elements, so rise of temperature above a fixed value must be prevented by cooling the semiconductor elements during operation of the equipment. Whether or not efficient cooling of the semiconductor elements can be achieved is therefore extremely important in regard to the performance of the equipment.
FIG. 1A and FIG. 1B are diagrams illustrating the layout of a conventional cooling device for a heat-generating element, FIG. 1A being a plan view and FIG. 1B being a cross-sectional view. In these Figures, heat-generating elements 101 are arranged in checkerboard (sometimes called “go” in Japanese) fashion on the surface of a heat sink 102. Heat sink 102 is formed of material of good thermal conductivity such as copper or aluminum and is formed with coolant passages 103 that have bending points at a plurality of locations in its interior.
Thus, when coolant 106 (for example a liquid such as water) is delivered from a coolant inlet 104, this coolant 106 advances in meandering fashion through the interior of coolant passage 103 so that cooling of the heat-generating elements 101 is performed in uniform fashion by the heat exchanging action of coolant 106 during this advance. After this heat exchanging has been completed, the coolant 106 is then discharged from coolant outlet 105 to outside heat sink 102.
It should be noted that, although in this prior art, the case was illustrated in which heat-generating element 101 were arranged in checkerboard fashion, heat-generating elements 101 could be arranged in a zigzag fashion. FIG. 2A and FIG. 2B are diagrams illustrating the differences between the checkerboard arrangement and the zigzag arrangement. In the checkerboard arrangement, as shown in FIG. 2A, the positions of heat-generating elements 101 are in an aligned arrangement in each column and each row; in the zigzag arrangement shown in FIG. 2B, the positions of heat-generating elements 101 in a given row and the positions of heat-generating elements 101 in the adjacent row are offset.
FIG. 3A and FIG. 3B are diagrams illustrating the arrangement of a conventional device different from that of FIG. 1A and FIG. 1B, FIG. 3A being a cross-sectional view in the front elevation direction and FIG. 3B being a cross-sectional view in the side direction. In these Figures, heat-generating elements 101 are incorporated as structural elements of module elements 107, and are arranged on a plate member 108. The periphery of a heat-generating element 101 is covered by a cover member 109 and the peripheral region of plate member 108 is mounted on heat sink 102 by means of mounting screws 110. In the same way as in the case of the prior art of FIG. 1A and FIG. 1B, the heat sink 102 performs cooling of heat-generating elements 101 by means of coolant 106, being formed with heat radiating fins 111 and a channel 112 constituting a passage for coolant 106.
Thus, in the cooling device shown in FIG. 3A and FIG. 3B, when the coolant 106 is fed in from coolant inlet 104, this coolant 106 advances through channel 112 between heat radiating fins 111 and cooling of the heat-generating elements 101 is uniformly effected by the heat exchange action of coolant 106 during this advance.
Although, as mentioned above, cooling of the heat-generating elements 101 is performed uniformly by the heat exchange action of cooling medium 106 flowing through the interior of heat sink 102, not withstanding this uniformity a certain degree of temperature difference is produced between portions where passage for coolant 106 is provided and portions other than these, so complete uniformity is not achieved.
Furthermore, with a conventional cooling device, the coolant 106 advances through coolant passages 103 or channels 112, so a certain time is unavoidably required for it to reach coolant outlet 105 from coolant inlet 104. Transiently, therefore, a large temperature difference can be produced between portions that have been reached by coolant 106 and portions that have not yet been reached thereby. For example, the distance of the two points P1 and P2 shown in FIG. 1A is short since these are positions on mutually adjacent heat-generating elements 101. However, since coolant passage 103 is of a meandering shape, even though the portion of point P1 is cooled by coolant 106, the portion of point P2 is still not yet cooled, so a condition in which there is a large temperature difference between the two points is produced. A large tensile heat stress is thereby generated between these, with the result that this heat stress is applied to the heat-generating element 101 also.